Polypropylene has various industrial applications, particularly it is widely applied for materials used in automobiles and electronic products, etc. with various usages. For more expanded applications of polypropylene, an improvement in rigidity which may be led by an increase in the degree of crystallinity is further required. In order to obtain such properties in polypropylene, it is needed for a solid catalyst for preparing the same to be designed to have high stereoregularity.
For polymerization of olefins such as propylene or the like, a solid catalyst comprising magnesium, titanium, an internal electron donor and halogen as essential elements is known in this field of art, and methods for polymerizing or copolymerizing olefins have been proposed many. However, such methods are not satisfying in terms of obtaining polymers having high stereoregularity with a high production yield, and thus needed to be improved in the above aspect.
In order to reduce the production cost by increasing the polymerization activity and improve physical properties of the resulted polymers by improving the catalyst performance such as stereoregularity, it is generally known in this field of art to use diester of aromatic dicarboxylic acid as an internal electron donor and related patent applications have been filed many, for examples, U.S. Pat. No. 4,562,173, U.S. Pat. No. 4,981,930 and the like. The above patents describe a method for preparing a catalyst showing high activity and stereoregularity by using aromatic dialkyldiesters or aromatic monoalkylmonoesters. However, diester compounds of an aromatic dicarboxylic acid are endocrine disruptors which may have critical effects on reproductive function disorders in eco-system including human, growth disorder, deformity, cancer and the like, even with an extremely small amount. In this regard, in the preparation of polypropylene used as a food package material, etc., currently there is an increasing need for using a catalyst which contains an internal electron donor made of an eco-friendly material. Further, the methods according to the above-mentioned patents cannot provide high stereoregular polymers with a high yield to the satisfying degree and thus further improvements in the methods are needed.
Korean Patent No. 0491387 discloses a preparation method for a catalyst using non-aromatic diether compound as an internal electron donor, and Korean Patent No. 0572616 discloses a preparation method for a catalyst using a non-aromatic compound containing both ketone and ether groups as an internal electron donor. However, the resulted catalysts by the methods according to the above two patents need to be significantly improved in stereoregularity and molecular weight distribution of polymers.
Although US patent publication No. 2009/0069510A1 proposes a method for preparing a catalyst using non-aromatic diisobutyl-4-methyl-cyclohexane-1,2-dicarboxylate, the resulted catalyst is needed to be improved in both activity and stereoregularity, and it does not disclose any examples of using bicyclic compounds.